It is difficult to determine golf ball spin axis through direct measurement. This disclosure provides a means and method to measure golf ball spin axis directly by making use of an appropriately spaced array of Doppler radar receivers.
Conventionally, the flight path of a golf ball is determined mainly by its launch speed, launch angle relative to the horizontal, and spin. Golf ball spin is caused by using a lofted club with a grooved club face. Spin imparts aerodynamic forces on a ball due to the interaction between the dimpled surface of the ball and the surrounding air fluid. In a golf ball, a lifting force opposite to gravity causes the ball to stay airborne longer and allowing a golfer to achieve greater carry distances than if no such force was present.
A golfer can also intentionally or unintentionally cause a golf shot to follow a horizontally curved trajectory if the ball spin axis is orientated to allow a lateral aerodynamic force to be generated.
Current Doppler radars use indirect methods to estimate golf ball spin axis. One example is to estimate the spin axis from analyzing the lateral curvature in the trajectory, and the horizontal trajectory, from which spin values can be estimated. This method is limited in that it has to observe the ball flight for an extended time period (not possible in an indoor test environment or fitting studio), and is affected by wind which disturbs the trajectory, and radar alignment errors. Another example is to measure the relative directions of the club and the ball at impact, and to calculate an estimate of the horizontal and lateral spin components that can result from the strike. Current camera-based systems are also used to measure golf ball spin axis. Cameras are generally poor at measuring high speed objects such as moving golf balls. High speed cameras are costly and suffer from difficulties in alignment, illumination, and measurement reliability. Many camera-based spin measuring systems also require some form of ball marking. Current methods also usually involve determining complex three-dimensional movement from limited and blurred two-dimensional images, leading to inaccurate results or even failing to provide a result.
This disclosure addresses these problems and provides a system and method to directly measure the ball spin axis from signals received in multiple spaced Doppler radar receivers.